单选题 Researchers have recently found a connection between disease and stressful situations. To test this theory, psychologists are trying to find a link between the brain and the immune system.
The immune system in our bodies fights the bacteria and viruses which cause disease. Therefore, whether or not we are likely to get various diseases depends on how well our immune system works. Biologists used to think that the immune system was a separate, independent part of our bodies. Recently, however, they have found that our brain can affect our immune system. This discovery indicates that there may be a connection between emotional factors, such as stress or depression, and illness.
Although many doctors in the past suspected a connection between emotional factor and disease, they had no proof. Scientists have only recently discovered how the brain and the immune system function. Before this, no one could see a link between them. As a result, medical science never seriously considered the idea that psychological factors could cause disease.
Several recent studies showed a connection between stress and illness, for example, researchers went to an American military school to study the students. They found that the sick students there had a lot of academic pressure and wanted to achieve, but they were not very good students. In a similar study, researchers studied a group of student nurses and found that the nurses who developed cold sores were the ones who described themselves as generally unhappy people.
In addition to these results, which support their theory, researchers are also looking for proof that stress can damage the immune system. Researchers studied recently bereaved people, i.e. , people whose loved ones have just died, because they are more likely to become ill or die. By examining the immune system of recently bereaved people, the researchers made an important discovery. They examined some white blood cells which are an important part of the immune system. They were not functioning properly. The fact that they were not working correctly indicates that severe psychological stress, such as a loved one"s death, may damage an important part of our immune system.
There is still no positive proof of a connection between the immune system and psychological factors. Researchers also say that the results of the studies on bereaved people could have a different explanation. For example, bereaved people often sleep and eat less than normal, or may drink alcohol or take medication. These factors can also affect the immune system. More research is needed to clearly establish the connection between the immune system and psychological factors.

单选题 The study on the military school students indicated that ______.

单选题 The immune system ______.

单选题 In the past, many doctors ______.

单选题 Which of the following is NOT TRUE according to the passage?

单选题 The text mainly supplies information for answering which of the following questions?